This application claim priority to German application No. 100 59 057.8, filed Nov. 28, 2000, herein incorporated by reference.
1. Field of Invention
The invention relates to the use of mixtures of organofunctionally modified polysiloxanes with branched alcohols in the production of flexible polyurethane foams.
2. Description of Related Art
Polysiloxane-polyoxyalkylene block copolymers, hereinafter referred to as polyether siloxanes, are used in the production of polyurethane foams. They make it possible to obtain a uniform, fine pore structure and stabilize the foam during the production process.
However, depending on the production process and depending on what further raw materials are used, an unsatisfactory cell structure is obtained in some cases. For example, the use of polyols having a high polypropylene oxide content frequently tends to give a coarser cell structure.
The equipment used can also lead to an irregular or coarse cell structure, for example when using low-pressure mixing heads or when the raw materials are simply mixed by stirring at atmospheric pressure.
The use of alternative blowing agents, in particular CO2, also places particularly high demands on the polyether siloxane in respect of achieving a fine-pored cell structure. Owing to the advantageous ecological balance, this liquid CO2 technology has become increasingly important in the past years. In this process, pressurized CO2 is used as blowing gas in addition to the CO2 formed by chemical reaction of the isocyanates used with water. This technology is described, for example, in EP-A-0 645 226. However, the introduction of this technology has shown that the spontaneous foaming of the pressurized CO2 on discharge of the reaction mixture places increased demands on the cell formation characteristics of the components used in the foam formulation. This can also be explained by the isocyanate/water reaction, which previously commenced slowly over a period of several seconds, leading only to slow saturation of the liquid phase with gas and thus the slow formation of gas bubbles, viz. the cream phase of the foam.
This previously slow process which forms the basis for the morphological properties, i.e. cell count and cell size distribution of the resulting foam is now compressed into fractions of a second, namely the time required by the raw materials to pass from the pressurized mixing bead of a foaming machine and the adjoining discharge device to the ambient pressures of one atmosphere. This results, in a manner similar to shaving foam from a spray can, to spontaneous formation of a foam due to vaporization of liquid CO2. The defects which occurred in such foams were nonuniform, sometimes enlarged cells within the foam structure, and the use of suitable foam stabilizers can be useful for minimizing these defects. Nevertheless, there is often the problem, depending on boundary conditions (pressure, raw material temperatures, use of solids in the formulation), of stabilizers which are well-suited according to the present state of the art, e.g. as described in U.S. Pat No. 5,357,018 or U.S. Pat. No. 5,321,051, not producing fully defect-free foams.
In principle, the cell structure can be made finer by increasing the amount of polyether siloxane used, but there is limited latitude for achieving this increase, firstly because of the accompanying phenomenon of overstabilization which then occurs and can lead to a high proportion of closed cells, in extreme cases even to shrinkage of the foam, and secondly because of the associated unfavorable economics.
In principle, the use of additives to polyether siloxanes or flexible foam formulations for increasing the fineness of the cells is already known.
EP-A-0 900 811 describes the use of cyclic carbonates as agents for increasing the fineness of the cells in flexible foam formulations. However, the cyclic carbonates are effective only in amounts of the same order of magnitude as the polyether siloxane and additionally have the disadvantage of being volatile components which vaporize from the finished foam.
EP-A-0 976 781 described the combined use of polyether siloxanes and salts of organic acids. The cells become finer even at low concentrations, but the solubility of the salts is relatively limited so that the use of water as cosolvent becomes necessary. The use of such combinations is therefore restricted to hydrolysis-stable polyether siloxanes. Furthermore, water contributes to the blowing reaction with isocyanates and may, depending on the concentration used, have to be taken into account in the formulation calculation.
U.S. Pat. No. 4,520,160 describes a process for preparing polyether siloxanes in the presence of fatty alcohols. The latter prevent gel formation during the preparation. The resulting products are preferably used as emulsifiers in cosmetic applications. The document also mentions the in-principle possibility, documented by means of an example, of use in polyurethane foams, but liquid CO2 applications are not mentioned. The use of the product described has, according to this document, no negative influence on the applications mentioned. On the basis of the information provided, the experiment described using a mixture of a polyether siloxane having an SiC structure and isostearyl alcohol gives an open-celled foam whose properties are equal to or better than a foam resulting from a comparative experiment in which isopropyl alcohol is used in place of isostearyl alcohol. Specific criteria for the assessment are not mentioned. In particular, no information on cell structure is given. The foam is only described by the characterization xe2x80x9cgood foamxe2x80x9d. Analysis of the example leaves the question of which class of polyurethane compounds is being addressed largely open, since, for example, the polyol type is not defined. The catalyst employed is the organotin compound dibutyltin dilaurate (DBTDL) which could indicate an HR slabstock application. DBTDL is frequently used in flexible foam applications exclusively in HR slabstock and not in conventional slabstock; the latter application requires tin octoate as catalyst. DBTDL is additionally employed in the production of rigid foams and also of elastomers/shoe soles, or classes of polyurethane different from flexible foams.
Our attempts to repeat the example lead not to a flexible foam but to a prepolymer-like elastomer without foam character. The use of a defined amount of water and amine catalysts would be absolutely necessary for producing a flexible foam.
Neither water nor amine catalyst are mentioned in the example; the product is thus not a flexible foam. The foam parameters described for the products of the experiment, e.g. foam height and air permeability, are thus not comprehensible.
The present invention relates to formulations for producing flexible polyurethane foams, by which are meant both conventional flexible polyether foams and flexible polyether foams produced with the aid of liquid CO2 technology.
Conventional flexible polyether foams are produced using as catalyst, apart from a tertiary amine, at least one of the following:
a) a metal salt of an organic acid, for example an alkali metal, alkaline earth metal, Al, Sn, Pb, Mn, Co, Bi or Cu salt of an organic acid such as octanoic acid, ricinoleic acid, acetic acid, oleic acid, lauric acid or hexanoic acid;
b) alkoxides and phenoxides of various metals, e.g. Ti(OR)4, Sn(OR)4, Sn(OR)2, Al(OR)3, where R are alkyl or aryl radicals;
c) chelate complexes of various metals with acetylacetone, benzoylacetone, trifluoroacetylacetone, ethyl acetoacetate, salicylaldehyde, cyclopentanone-2-carboxylate, acetylacetonimine, bisacetylacetone alkylenimines, salicylaldimine and the like, with possible metals being Be, Mg, Zn, Cd, Pb, Ti, Zr, Sn, As, Bi, Cr, Mo, Mn, Fe, Co, Ni or ions such as MoO2++ and UO2++ and the like;
d) acidic metal salts of strong acids, e.g. iron chloride, tin chloride, antimony trichloride and bismuth chloride or nitrate.
The polyols suitable for flexible foams are usually polyether polyols as are described, for example, in U.S. Pat. No. 3,346,557 and polymer polyols as are described, for example, in U.S.-Re-28,715 and U.S. Pat. No. 3,346,557, U.S. Pat. No. 3,823,201, U.S. Pat. No. 3,850,861, U.S. Pat. No. 4,454,255, U.S. Pat. No. 4,458,038, U.S. Pat. No. 4,50,194, U.S. Pat. No. 4,390,645 and also U.S. Pat. No. 4,431,754. The polyols which are preferably employed are trifunctional and have predominantly secondary OH groups.
It is an object of the present invention to provide, inter alia, improved stabilizer systems in the production of flexible polyurethane foams.
It has surprisingly been found that synergistically acting mixtures of polyether siloxanes with small amounts (from 0.1 to about 30%, preferably from about 5 to about 10%,. based on the polyether siloxanes) of branched fatty alcohols and derivatives thereof have a significantly more effective influence on reducing the size of the cells than do the polyether siloxanes alone. The simultaneous use of the constituents of the mixture is of critical importance. Separate introduction of the branched fatty alcohol, for example via the polyol component, does not lead to the desired effect. The mixtures claimed may further comprise solvents such as a monool, diol or triol of a polyether, a glycol having a low molecular weight or a nonionic surfactant. The solvents themselves have no influence on the surface-active properties of the polyether siloxane in the flexible foam formulation per se, but represent a material which is chemically reactive in the polyurethane formulation and may be present in the mixture claimed.
Polyether Siloxanes:
The polyether siloxanes on which the present invention is based are polysiloxane-polyoxyalkylene copolymers comprising modified polyoxyalkylene building blocks.
The invention, in principle, relates to all structures which can be used generally in the production of flexible polyurethane foams. However, an important factor for the synergistic action of the two components of the mixture is the use of a polyether siloxane which preferably has a certain nucleating action, i.e. gives a satisfactory cell structure even when used alone. In contrast, polyether siloxanes which when used alone give a coarse cell structure frequently do not allow production of synergistically active mixtures in the sense of the invention.
For example, hydrophobic stabilizers are particularly suitable for achieving a fine cell structure, while on the other hand hydrophilic representatives lead, as a result of their structure, to a rather coarse cell when employed alone or in a mixture with the alcohol used according to the invention.
The polyoxyalkylene block can be linked to the polysiloxane via a hydrolysis-stable SiC bond or via a less hydrolysis-stable SiOC bond.
The number of siloxane units in the polysiloxane and the number of possible linkages with the polyoxyalkylene can be altered in virtually any desired way.
Polysiloxane-polyoxyalkylene block copolymers are described in numerous publications.
For example, DE -A-15 70 647 describes SiOC-linked polyether siloxanes. The preparation of this class of polyether siloxanes is described in, for example, DE-A-10 12 602, DE-A-10 40 251, DE-A-11 20 147and U.S. Pat. No. 3,115,512.
The preparation of SiC-linked polysiloxane-polyoxyalkylene block copolymers is described, for example, in U.S. Pat. No. 2,846,458 and in DE-A-12 20 615 and DE-A-11 53 166.
The polyether siloxanes used in the present invention have the formula I, 
where the radicals
R1 are alkyl radicals or aryl radicals,
R2 are R1 and/or R3 and/or R4,
R3 is a polyether radical of the formula II
xe2x80x94(Y)e[O(C2H4xe2x88x92dRxe2x80x2dO)m(CxH2xO)pZ]wxe2x80x83xe2x80x83(II)
xe2x80x83with the proviso that
e=0 to 1,
w=to 4,
d=1 to 3,
mxe2x89xa71,
x=2 to 4, whereby x is 2, 3 and/or 4 in the same polyether radical; i.e., x is such that a polyether radical may contain C2H4Oxe2x80x94, C3H6Oxe2x80x94 and C4H8O units either individually or in combination, and
pxe2x89xa71, and
Y is a (w+1)-valent hydrocarbon radical which may be branched,
Rxe2x80x2 is selected from the group consisting of monovalent, aliphatic or aromatic hydrocarbon radicals preferably having from 3 to 18 carbon atoms,
Z is hydrogen or a monovalent organic radical including an acyl radical, the sum m+p=1 to 150,
R4 is a polyether radical of the formula III
xe2x80x94(F)f[O(CxH2xO)rZ]gxe2x80x83xe2x80x83(III)
xe2x80x83with the proviso that
f=0 or 1,
x=2 to 4,
g=1 to 4 and
rxe2x89xa71,
F is a (g+1)-valent hydrocarbon radical which may be branched,
a is from 1 to 100 when b is from 6 to 8,
a is from 1 to 200 when b is from 3 to 6,
a is from 1 to 300 when b is from 0 to 3,
b 0 to 8.
For the purposes of the present invention, particular preference is given to using polysiloxanes of the formula I in which the indices e and/or f=0. These are accordingly SiOC structures.
For the purposes of the present invention, particular preference is given to using polyether siloxanes of the formula I in which R2 in at least one case is R3, with the proviso that m greater than p.
Alternatively, preference is in the same way given to using polysiloxanes of the formula I in which the indices e and f=1. These are accordingly SiC structures.
The alcohols and derivatives thereof on which the invention is based are compounds of the formula IV
Rxe2x80x94CH2xe2x80x94Oxe2x80x94Rxe2x80x2xe2x80x83xe2x80x83(IV)
where
R=a branched alkyl radical having at least 7 carbon atoms and preferably up to 26 carbon atoms and
Rxe2x80x2=H, acyl or R3 as defined above.
The branched alcohols and derivatives of the formula IV used in the present invention have an alkyl chain R of at least 8 carbon atoms, with the proviso that the chain has at least one branching point.
The alcohols and derivatives used do not have to have surfactant character in order to achieve the effect produced according to the invention.
Examples of compounds claimed are the commercially available Guerbet and Ziegler alcohols and also naturally branched oxo and isotridecyl alcohols.
For the purposes of the present invention, particular preference is given to using the mixture of polysiloxane of the formula I and branched alcohol in the production of flexible polyurethane foams comprising liquid carbon dioxide as blowing agent.
For the purposes of the present invention, particular preference is given to using the mixtures of polysiloxane of the formula I and branched alcohol and derivatives thereof of the formula IV in an amount of from about 0.3 to about 3%, based on the flexible polyurethane foam formulation.
The present invention further provides mixtures of organofunctional modified polysiloxanes of the formula I 
where the radicals
R1 are alkyl radicals or aryl radicals,
R2 are R1 and/or R3 and/or R4,
R3 is a polyether radical of the formula II
xe2x80x94(Y)e[O(C2H4xe2x88x92dRxe2x80x2dO)m(CxH2xO)pZ]wxe2x80x83xe2x80x83(II)
xe2x80x83with the proviso that
e=0 to 1,
w=1 to 4,
d=1 to 3,
mxe2x89xa71,
x=2 to 4, whereby x is 2, 3 and/or 4 in the same polyether radical; i.e., x is such that a polyether radical may contain C2H4Oxe2x80x94, C3H6Oxe2x80x94 and C4H8O units either individually or in combination, and
pxe2x89xa71, and
Y is a (w+1)-valent hydrocarbon radical which may be branched,
Rxe2x80x2 is selected from the group consisting of monovalent, aliphatic or aromatic hydrocarbon radicals, preferably having from 3 to 18 carbon atoms,
Z is hydrogen or a monovalent organic radical including an acyl radical, the sum m+p=1 to 150,
R4 is a polyether radical of the formula III
xe2x80x94(F)f[O(CxH2xO)rZ]gxe2x80x83xe2x80x83(III)
xe2x80x83with the proviso that
f=0 or 1,
x=2 to 4,
g=1 to 4and
rxe2x89xa71,
F is a (g+1)-valent hydrocarbon radical which also may be branched,
a is from 1 to 100 when b is from 6 to 8,
a is from 1 to 200 when b is from 3 to 6,
a is from 1 to 300 when b is from 0 to 3,
b=0 to 8,
with the proviso that at least one of the indices e and/or f=0, and branched alcohols and derivatives thereof of the formula IV
Rxe2x80x94CH2xe2x80x94Oxe2x80x94Rxe2x80x2xe2x80x83xe2x80x83(IV)
xe2x80x83where
R=a branched alkyl radical, preferably having from 7 to 26 carbon atoms and
Rxe2x80x2=H, acyl or R3 as defined above.